Syndesmosis injury is not a term you will hear very often, sometimes it may be labeled as a “high ankle sprain”, other times it may be completely misdiagnosed as a Peroneus longus tear or shin splints. The syndesmosis is a part of the human body which sits very deep anatomically and is aptly forgotten about due it merely being considered as connective tissue which lies between the fibula and tibia.
In this article we will investigate the syndesmosis as a structure, common injuries or movement patterns associated with the injury and treatment options available.

Ankle joint injuries account for 10-30% of all single sport injuries within the athletic population. The syndesmosis of the lower leg is a made up of four ligaments which overlapping architecture provide significant joint stability. As our knowledge about anatomy and pathological stresses increase we begin to understand where an initial injury may have coincided with a secondary injury or perhaps caused one; that is why in recent years syndesmotic injury prevalence has moved from between 1-18% of ankle injuries to between 17 – 74 % of all ankle sprains in young athletes. A lateral ankle sprain is commonly described as the moment in which a foot undergoes both excessive plantarflexion and inversion further information about lateral ankle sprains can be seen here: https://footnotesblogging.com/2014/06/11/ankle-sprains-lateral-ligaments-instability-and-rehabilitation/

Syndesmosis develops as a result of traumatic forces which give rise to the disruption of the distal tibiofibular joint articulation ending in syndesmotic rupture. These forces are commonly a result of rotational torque penetrating the syndesmotic complex of the fibular or a moment of bending and rotation with an increase in the axial load. The syndesmosis is believed to have a much longer recovery period than that of a lateral ankle sprain, with estimates being anywhere from 2-30x as long dependent on the severity. Sman, et al found that syndesmotic injury recovery was four times longer than that of a lateral ankle sprain of equivalent grading.

The ankle joint undergoes significant stress and loading during both daily and competitive activity with the equal of six times body weight being place through the joint. Failure of the ankle joint complex at any time has the potential to create instability and increase pain locally. The ligaments of the ankle joint are responsible for the stabilization of the syndesmosis by reducing lateral displacement of the fibula which is important given the unstable nature of the foot as it moves through the triplanar movement pattern from plantarflexion through to dorsiflexion.

Clinical tests in the identification of syndesmosis injury can be found below;
1. Localized tenderness if palpation of the anterior inferior tibio-fibular ligament.
2. Pain with passive ankle joint dorsiflexion due to the widening of the mortise, eliciting pain in the region.
3. External rotational stress test using rotation of the talus.
4. Squeezing the middle of the lower leg with the intention of compressing the fibular toward the tibia and noting pain or discomfort.
5. Talar transition test
6. Degree of motion of the fibular in the sagittal place relative to the tibia and eliciting pain.

Further observations include whether the patient is able to weight bear, discoloration or bruising in the area of the syndesmosis and a positive anterior draw test with the knee at 90 degrees flexion and a display of laxity inferring both ATFL and CFL rupture. The presence of the latter two observations is 98% sensitive and 94% specific of 84% of acute lateral ligament ruptures.

It is believed that most syndesmotic injuries are caused by the external rotation of the lower leg resulting in the widening of the mortise and separating the tibia and fibular causing a strain of the syndesmosis and initial disruption to the anterior inferior tibiofibular ligament. However there is no way of duplicating this mechanism to develop evidence. Additionally no significant correlation has been seen between the mechanism of action and the severity of the injury itself. When preparing to begin intervention it is important to detail the time lapse between completion of injury and the evaluation as this can affect the treatment choices. A simple classification as follows will suffice;

True evaluation of the syndesmosis requires three radiographical views; AP, lateral and mortise of the ankle in a weight bearing position to provide the best possible report of suspected injury. Additionally, in the case of more subtle injury a CT or MRI may be more appropriate dependent on the individual. Syndesmosis injury can be classified into three categories which may require different approaches in the management protocols.

No or slight evidence of instability with tear of AITFL and partial tear of IOL

Use of offloading boot 6-8 weeks and seek surgical opinion.
Followed by assisted rehabilitation

III

Definite instability with complete tear of the syndesmotic ligaments

Surgical intervention required (see surgery explanation below)

Surgical intervention is commonly required for the grade 3 syndesmosis injury and at times for a grade 2 injury also. The most commonly used surgical intervention is fixation about 30-40mm above the tibiofibular joint, which has been proven to be more advantageous over fixation 20-30mm or the 40-45mm marks. Additionally, if a patient is suspected of a syndesmosis injury and required to undergo a arthroscopy of the ankle joint it is possible for a definitive diagnosis to be made with the use of a 3mm cinematic probe. Furthermore, it is suggested that the patient receive post-operative CT scans due to the correlation with malreduction in the mortise and functional outcomes.

After surgery and a significant reduction in pain any biomechanical issues can be addressed as deemed necessary and lower limb weaknesses improved with a rehabilitation program suitable for the individual patient. Once again an example of a lateral ankle sprain program can be found here: https://footnotesblogging.com/2014/06/11/ankle-sprains-lateral-ligaments-instability-and-rehabilitation/
As you can see a few simple assessments can be completed to rightfully identify a syndesmosis injury before imaging is even complete. Treatment options can be kept primarily conservative for the most part and return to sport is much faster if the actual injury is identified early as opposed to misdiagnosis or flippant assumption of it being an “ankle sprain”.